1. Field of the Invention
The present invention relates generally to the field of data compression, and more specifically to a method and system for real-time multiple-pass data encoding, and particularly, for encoding video signals.
2. Description of the Prior Art
Digital video compression is an essential technology in video communications, broadcasting, and storage. MPEG video coding standards have been successfully used to reduce the transmission bandwidth and storage space requirements in many applications, such as digital TV broadcast through satellite and cable, Digital Video Disk (DVD), Video on-Demand and video streaming over the Internet, etc. However, emerging applications and new services become increasingly demanding for less transmission bandwidth and storage space. For example, in Video-on-Demand service over Asymmetric Digital Subscriber Line (ADSL), live news and sports events are transmitted in real-time to the subscribers using MPEG-2 video coding standard (ISO/IEC 13818-2) at a constant bit rate (CBR) in the range of 0.6 to 2 Mbits/second. For MPEG CBR video encoding at such a bit rate range, it is very challenging for the conventional MPEG encoders available on the commercial market to produce acceptable picture quality. Conventional MPEG encoders employ a single encoder scheme as depicted in FIG. 1. As shown in FIG. 1, the conventional video encoder device 110 implements a coding strategy which is based on the information retained in coding only the previous video frames 100 to provide coded video output 120. These encoders 110 routinely adopt a coding strategy that is only based on the information obtained in coding of the previous video frames 100 and/or rely on some assumed signal models to predict or estimate the signal properties of the current input frame to guide the encoding process of the current frame. However, natural video is a statistically non-stationary signal source. Prediction and estimation based on the past signal will not correctly describe the current input signal. In addition there is no known robust signal model that can describe the natural video signal reliably. Such encoders will not be able to determine and apply the best coding strategy to encode the incoming video frames for lack of the information about the current and future input frames. In order to meet the challenges from more demanding emerging applications, more sophisticated schemes for MPEG-2 video coding are needed to improve the performance and to ensure the quality of services.
Research efforts have been made to improve the variable bit rate (VBR) MPEG video coding, e.g., for DVD applications, by employing two-pass and re-encoding schemes. However, there are no published research results for multi-pass CBR coding in the literature.
It would thus be highly desirable to provide a real-time MPEG CBR video coding method and associated system that are able to jointly determine and apply the best coding plan to encode input video frames based not only on the information of the previous and current frames, but also the information about the future input frames.